High energy laser beam director system and method

ABSTRACT

A beam director subsystem and method for use in a weapons system. The beam director subsystem includes a source of electromagnetic radiation for generating a high energy laser (HEL) beam. The electromagnetic radiation is directed to a secondary mirror that reflects the electromagnetic radiation to a primary mirror for output of the HEL beam. The secondary mirror is generally curved and expands the electromagnetic radiation received from the source prior to outputting the HEL beam from the primary mirror. The subsystem further includes a track telescope coupled to the housing. The track telescope has a track detector configured to receive electromagnetic radiation originating from the HEL and electromagnetic radiation emitted from an illuminator and reflected from an airborne target.

TECHNICAL FIELD

The present invention relates generally to a high energy laser (HEL)beam director system and method for directing a HEL beam at an intendedtarget.

BACKGROUND OF THE INVENTION

Directed energy weapons and specifically high-energy laser (HEL) weaponsare being considered for variety of military applications with respectto a variety of platforms, e.g., spaceborne, airborne and land basedsystems to name a few. These weapons generally involve the use of alaser or other source of a high-power beam of electromagnetic radiationto track and destroy an intended target. To achieve mission objectives,directed energy weapons must accurately track the intended target andmaintain a HEL beam on the target until an intended outcome is achieved.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a beam director system andmethod for aiming a high energy laser (HEL) beam at an intended target.The beam director system includes a source of electromagnetic radiationfor generating a HEL beam. A secondary mirror receives theelectromagnetic radiation from the source and reflects theelectromagnetic radiation to a primary mirror for output of the HELbeam. The secondary mirror is generally curved and expands theelectromagnetic radiation received from the source of electromagneticradiation prior to outputting the HEL beam from the primary mirror. Ahousing generally houses the primary mirror and the secondary mirror andHEL beam is output through an end of the housing. An illuminator fortracking the intended target may be attached to the housing. Theilluminator generates electromagnetic radiation to be reflected by thetarget and detected by the tracking detector. A track telescope may alsobe attached to the housing. The track telescope includes a trackdetector secured at one end to receive a first portion of theelectromagnetic radiation and a second portion of the HEL beam, as wellas electromagnetic radiation reflected from the target. A processor iscoupled to the track detector and a steering controller of the HEL beamfor processing the first portion and second portions of theelectromagnetic radiation and the reflected electromagnetic radiation tosteer the HEL beam at the intended target.

One aspect of the invention relates to a beam director system including:a source of electromagnetic radiation for generating a high energy laser(HEL) beam; a secondary mirror for receiving the electromagneticradiation and reflecting the electromagnetic radiation to a primarymirror for output of the HEL beam through a housing, wherein thesecondary mirror is curved and expands the electromagnetic radiationreceived from the source prior to outputting the HEL beam from theprimary mirror; a track telescope coupled to the housing, wherein thetrack telescope has a track detector configured to receive a firstportion of the electromagnetic radiation of the HEL; and a processorcoupled to the track detector and a steering controller of the HEL beam,wherein the processor processes the first portion of the electromagneticradiation to steer the HEL at an associated target.

Another aspect of the invention relates to a method of aiming a highenergy laser (HEL) beam, the method including: generatingelectromagnetic radiation for use as a HEL beam to be directed at anairborne target from a source of electromagnetic radiation; reflectingthe electromagnetic radiation off of a secondary mirror and a primarymirror for output of the HEL beam through a terminal end of a housing,wherein the secondary mirror is curved and expands the electromagneticradiation received from the source prior to outputting the HEL beam fromthe primary mirror; detecting a first portion of the HEL beam prior tooutput from the terminal end of the housing at a track detector;processing the first portion of the HEL beam to control a steeringcontroller of the HEL to steer the HEL at an associated target.

The foregoing and other features of the invention are hereinafter morefully described and particularly pointed out in the claims, thefollowing description and the annexed drawings setting forth in detailillustrative embodiments of the invention, such being indicative,however, of but a few of the various ways in which the principles of theinvention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Likewise, elementsand features depicted in one drawing may be combined with elements andfeatures depicted in additional drawings. Moreover, in the drawings,like reference numerals designate corresponding parts throughout theseveral views.

FIG. 1 is schematic block diagram of an exemplary weapon system inaccordance aspects of the present invention.

FIG. 2 is schematic block diagram of a beam director subsystem inaccordance aspects of the present invention.

FIG. 3 is a schematic diagram of electromagnetic radiation paths of thebeam director subsystem of FIG. 2.

FIG. 4 is an exemplary housing for the beam director subsystem of FIG.2.

FIG. 5 is schematic block diagram of the exemplary weapon system inaccordance aspects of the present invention.

FIG. 6 is an exemplary block diagram of a mortar detection algorithm inaccordance with one aspect of the present invention.

FIG. 7 is an exemplary raw image of a mortar shell in accordance withaspects of the present invention.

FIG. 8 is an exemplary illustration of the mortar shell of FIG. 2 beingprocessed by a band-limited gradient operation in accordance withaspects of the present invention.

FIG. 9 is an exemplary of a mortar shell illustrating a shift of a highenergy laser (HEL) between two images in accordance with aspects of thepresent invention.

FIG. 10 illustrates an exemplary estimation of the shift from a previousimage to the current image in accordance with aspects of the presentinvention.

FIG. 11 illustrates an exemplary threshold and centroid track with anHEL spot identified in the center of mortar shell in accordance withaspects of the present invention.

FIG. 12 illustrates an exemplary threshold and centroid with an HEL spotidentified offset from the center of the mortar shell in accordance withaspects of the present invention.

FIG. 13 is an exemplary block diagram of a mortar tracking algorithm inaccordance with one aspect of the present invention.

FIG. 14 is an exemplary block diagram of a unmanned aerial vehicletarget pose detection algorithm in accordance with one aspect of thepresent invention.

FIGS. 15A-15D illustrate one or more principles of operation of the beamdirector subsystem in accordance with aspects of the present invention.

FIG. 16 is a HEL beam steering architecture in accordance with aspectsof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure relates to a beam director subsystem for use in aweapons system. The beam director subsystem includes a source ofelectromagnetic radiation for generating a high energy laser (HEL) beam.The electromagnetic radiation is directed to a secondary mirror thatreflects the electromagnetic radiation to a primary mirror for output ofthe HEL beam. The secondary mirror is generally curved and expands theelectromagnetic radiation received from the source prior to outputtingthe HEL beam from the primary mirror. The subsystem further includes atrack telescope coupled to the housing. The track telescope has a trackdetector configured to receive electromagnetic radiation originatingfrom the HEL. The beam director subsystem further includes anilluminator for targeting the airborne target. The illuminator generateselectromagnetic radiation to be directed at an airborne target. The beamdirector subsystem also includes a track detector coupled to the tracktelescope to receive electromagnetic radiation reflected from theairborne target.

A processor is coupled to the track detector and a steering controllerfor a high energy laser (HEL) to generate a control signal for input tothe steering controller in order to steer the HEL based at least in parton the received electromagnetic radiation. The processor processes thetarget information for tracking the airborne target based at least inpart on the received electromagnetic radiation detected from the trackdetector in a predetermined manner. The processor also processes one ormore portions of the HEL beam for alignment purposes.

A problem to be solved by the claimed invention is to autonomously tracka non-cooperative target and steer, focus, and maintain a high-energylaser beam on a predetermined aimpoint until a desired effect isobtained, which may include sensor denial, sensor destruction, warheaddestruction, structural failure of the target, etc. The claimed HEL beamdirector, when attached to a suitable radar guided gun system (e.g.,close in weapons system or similar coarse steering mechanism) providessuch functionality. The claimed system includes a beam expandertelescope that installs in CIWS gun mount, a integral off-axis targetacquisition and tracking system, which accepts a high-energy laser fiberinput, and controls focus and direction of the outbound laser energy byuse of inertial reference instruments and steering mirrors to impartlethal or disabling effects on the target.

A simplified schematic of a High Energy Laser (HEL) weapon system 10 isillustrated in FIG. 1. The HEL weapon system 10 includes a beam directorsubsystem 12, a radar 14 that detects objects (e.g., mortar shells,Unmanned aerial vehicles (UAVs), etc.) in a field (F), and a base 16that may be secured to a stationary (e.g., a fixed location on amilitary base) and/or moving platform (e.g., a tank, ship, etc.) tosecure the weapon system.

Referring to FIG. 2, the beam director subsystem 12 generates a HEL beam18 for use in incapacitating an intended target and/or otherwisedestroying an intended target. The beam director subsystem 12 includesHEL beam system and a tracking system. The HEL beam director subsystem12 provides the guidance and control of the HEL for the weapon system.

The beam director subsystem 12 includes a source of electromagneticradiation 20 for generating a high energy laser (HEL) beam. A secondarymirror 22 receives the electromagnetic radiation and reflects theelectromagnetic radiation to a primary mirror 24 for output of the HELbeam through the housing 26. The secondary mirror 22 is curved andexpands the electromagnetic radiation received from the source prior tooutputting the HEL beam from the primary mirror 24. The secondary mirror22 and/or the primary mirror 24 may be manufactured from aluminum or anyother material that is capable of withstanding the thermal andperformance demands of the present invention.

The secondary mirror 22 may be secured by a bracket 23 to one or morelinear actuators 25. The linear actuators 25 have an adjustable lengththat may be controlled to automatically change the distance between theprimary mirror 24 and the second mirror 22, which changes the focalpoint of the HEL beam. The linear actuators may be secured to thehousing and/or strut diverters 50, as illustrated in FIG. 2. In oneembodiment, there may be three pairs of linear actuators 25 secured tothe bracket 23 to allow adjustment of the secondary mirror 22.

The beam director subsystem 12 includes a track telescope 28 coupled tothe housing 26. The track telescope 28 has a track detector 30configured to receive a first portion and a second portion of theelectromagnetic radiation of the HEL beam, as discussed below. The tracktelescope 28 and the track detector 30 are also configured to receiveelectromagnetic emitted by an illuminator 32 and reflected off anintended target. A processor 34 is coupled to the track detector 30 anda steering controller 36 to control the HEL beam. The processor 34processes the first and second portions of the HEL beam along with theelectromagnetic radiation reflected from the intended target to steerthe HEL at the intended target.

The HEL beam 18 may be any type of high energy laser that is capable ofradiating electromagnetic radiation in a form to destroy and/or disableone or more intended airborne targets. The HEL 18 includes a source ofhigh energy electromagnetic radiation 20. The source of high energyelectromagnetic radiation 20 may be any type of electromagneticradiation that may be used to destroy and/or disable an airborne target.The electromagnetic radiation may be output at any power and frequencythat is operable to reduce and/or eliminate the threat of the airbornetarget. For example, the electromagnetic radiation may have a power of50 kW at 1070 nanometers.

The high-power electromagnetic radiation may be output from a fibercoupling 38 to a mirror 40. The mirror 40 may reflect theelectromagnetic radiation to an annular mirror 42. Multipleelectromagnetic radiation pathways will now be described.

One path of electromagnetic radiation reflects off the annular mirror 42to the fast steering mirror 44. The electromagnetic radiation thenreflects off fast steering mirror 44 to the beam-walk corrector mirror46. Referring to FIGS. 2 and 3, the electromagnetic radiation reflectsoff the beam-walk corrector mirror 46 through a void (V) formed in thecenter of primary mirror 24, reflects off secondary mirror 22, whichdistributes the electromagnetic radiation along the primary mirror 24for output through an open end 48 the housing 26. The output of the HELbeam 18 may also pass through strut diverters 50.

In another path of electromagnetic radiation, the annular mirror 42removes the core of the beam (e.g., the central portion of the reflectedbeam) and bypasses the primary mirror 24 so that the HEL energy is notreflected through the system 12 off the secondary mirror 20, as shown inFIGS. 2 and 3. In order to reduce heat, stray illumination redirectedout front end 48 of the housing 26. The beam director subsystem 12includes the following controls for stray light management and thermalmanagement: all-reflective fiber output coupler mirrors (not lenses),which manage high heat load better than lenses; the secondary mirror isa stop of optical system; radiation past edges exits front end 48 ofhousing 26 at a maximum angle less than 40 degrees; reflections offsecondary obstruction avoided by adding a hole in fold Mirror andreflecting stray light out of front end 48; reflector is positionedoutside of primary HEL signal path, mirrored support tube, and V-groovestrut guards 50 spread and manage stray light to be eye safe at apredetermined distance, and reduces heating of secondary mountingstructure for securing the secondary mirror 22 to the housing 26.

Another path of electromagnetic radiation includes a reflecting surface52 (e.g., a pentaprism) that routes a first portion of theelectromagnetic radiation of the HEL beam 18 through the track telescope28 to the track detector 30. The first portion of the electromagneticradiation is illustrated as being output from the upper portion of theprimary mirror 24. Between the reflecting surface 52 and the trackdetector 28 may be another reflecting surface 54 (e.g., a pentaprism) todirect the first portion of the electromagnetic radiation of the HELbeam through the track telescope 28 to the track detector 30. Apentaprism gives a perfect 90 degree rotation of the beam. The beamentering is output at 90 degrees relative to the incoming beam. Thereflecting surfaces 54, 56 are generally not affect rotations in plane.The output beam is not affected by rotation in plane. Thus, thereflecting surfaces 54, 56 provide precision reference in one direction.

In yet another electromagnetic radiation path, a reflecting surface 58(e.g., a lateral transfer hollow retroreflector, corner reflector, etc.)routes a second portion of the electromagnetic radiation of the HEL beam18 through the track telescope 28 to the track detector 30. The secondportion of the electromagnetic radiation is illustrated as being outputfrom the lower portion of the primary mirror 24. Between the reflectingsurface 58 and the track detector 30 may be another reflecting surface60 (e.g., a lateral transfer hollow retroreflector, corner reflector,etc.) to direct the second portion of the electromagnetic radiation ofthe HEL beam 18 through the track telescope 28 to the track detector 30.A lateral transfer hollow retroreflector gives a precise measure in twoaxes and parallelism is not affected by yaw and clocking rotations.Coupling of the reflecting surfaces 54, 56 and 58, 60 to detection bythe track detector 30 provides unambiguous indication of beam focus andtilt error between the two telescopes (e.g. housing 26 and tracktelescope 28).

Referring to FIG. 2, the beam director subsystem 12 further includes anilluminator 32 for generating electromagnetic radiation to be directedat the associated target. The illuminator 32 may be any type of a devicethat is capable of directing electromagnetic radiation to an intendedairborne target. The illuminator may output electromagnetic radiation atany desired frequency in the electromagnetic spectrum. In oneembodiment, the illuminator 32 is a laser diode array. The laser diodearray may output electromagnetic radiation in the infrared region of theelectromagnetic spectrum. For example, the laser diode array may a beamof electromagnetic radiation having output power of 100 Watts at awavelength of 808 nanometers.

The beam director subsystem 12 further includes a track telescope 28.The track telescope 14 includes one or more components 70A, 70B todirect electromagnetic radiation reflected from the intended airbornetarget and the first and second portions of electromagnetic radiationreceived from the HEL beam to the track detector 30. The track telescope28 generally gathers the reflected electromagnetic radiation and mayalso magnify the target and/or portions of the HEL beam. The exemplarycomponents 70A, 70B may vary based upon the type of electromagneticradiation being detected and/or telescope type, for example. Thecomponents 70A, 70B may include a lens and/or mirror that gathers light(or other electromagnetic radiation) and concentrates it so the imagecan be examined and/or further processed.

The track detector 30 may be any detector that is capable of capturingthe electromagnetic radiation reflected from the target and receive thefirst and/or second portions of electromagnetic radiation from the HELbeam 18. Generally, the track detector 30 has an array of pixels thatmay be used to calculate and/or characterize error, alignment, etc. Thedetector 30 may vary based on the electromagnetic spectrum employed bythe illuminator 32 and/or the HEL beam 18. In one embodiment, thedetector 30 may be a camera that is capable of detecting electromagneticradiation from the visible and/or infrared electromagnetic spectrum. Theelectromagnetic radiation detected by the detector 30 may be in the formof one or two dimensional images, for example.

The detector 30 is configured to receive electromagnetic radiationemitted from the illuminator 62 and reflected from the airborne target.In addition, the detector also receives electromagnetic radiationemitted from the HEL beam 18 through the primary mirror 24 and reflectedto the detector through reflecting surfaces 52, 54 and 58, 60, asdiscussed above. The detector 30 maintains knowledge of the alignment ofthe track telescope beam (e.g., the illuminator) and the HEL beam bymeasuring and processing incident light received with processor 34.

The processor 34 may be any type of computer that is capable ofcontrolling and processing data and electromagnetic radiation asdescribed herein. The processor 34 may also include a steeringcontroller 36 that couples the detector 30 and processor 34 to one moredevices (e.g., gyroscope 80, 82) for steering and/or aligning the HELbeam 18.

Although not shown for purposes of clarity, one of ordinary skill in theart will readily appreciate that the one or more beam splitters and/orabsorptive baffles may also be incorporated at or near various opticaland/or reflective components of the beam director subsystem 12 in orderto dissipate energy spilled over the edge of the reflective components.For example, one or more beam splitters may be placed in the opticalpath between the reflecting elements 52, 54 and 58, 60 so that a desiredsignal for the HEL beam is routed to the detector.

Referring to FIGS. 4 and 5, the beam director subsystem 12 may besecured to a weapons system 10. The housing 26 of the beam directorsubsystem 12 may be formed of a highly rigid material (e.g., aluminum,titanium, etc.). The housing 26 generally includes one or moreattachment members 80, as shown in FIG. 3. The attachment members 80 maybe flanges that extend on opposite sides of the housing 12. Theattachment members 80 engage the weapon systems and are secured by oneor more securing members through one or more holes 82 formed in theattachment members 70. Exemplary securing members may include bolts,screws, rivets, etc.). Generally any securing member that allows thebeam director subsystem to be installed and/or removed from weaponssystem 14 is deemed to fall within the scope of the present invention.

The gyroscope triads 100, 102 (FIG. 2) are the primary instruments formaintaining sensor to laser bore sight alignment. In general, theprocessor 34 processes the electromagnetic radiation received at thedetector 30 and outputs a corresponding signal to steering controller36, which controls operation of the gyroscopes 100, 102. The gyroscope100 is coupled to the housing 26 and is used to control alignment of theHEL beam 18. The gyroscope 102 is mounted to the track telescope and isused to control the track telescope 28. The gyroscopes 100, 102 aredebiased by on-line drift estimation using measurements available fromthe weapon system (such azimuth measurements and elevation alignmentmeasurements, and optical feedback from the retroflectors 58, 60 andprocessing through Kalman filter, as discussed below.

The signals received by the detector 30 may be processed by one or morealgorithms to determine alignment differences between the tracktelescope 28 and the HEL beam 18.

Referring to FIG. 6, a block diagram of signal flow associated with amortar detection algorithm 150 is illustrated. Data from the detector 30is input into block 152, which removes speckle and hot-spots detected inthe data. Generally, the data is in the form of raw image and input intoblock 152. One of ordinary skill in the art will readily appreciate thatthe image may be a raw image and/or include some processing of the imageprior to entry into the block 152.

At block 152, the data is filtered to remove or attenuate values thatare above and/or below a threshold. Such values may be caused by speckleand/or hot spots in the detected image. For example, data that is abovethe average intensity of the image may be clipped and/or attenuated.FIG. 7 is an exemplary illustration of an airborne target that has beenprocessed according to block 152. Note: the degree of lightness of areasnear the tail, which generates the most heat on the target.

At block 154, a fast Fourier transform is performed on the filtereddata, which converts the data from the spatial domain to a frequencydomain.

At block 156, a band-limited gradient operation is performed on thedata. The band-limited gradient operation removes the low frequenciesand high frequencies detect the in the image, so that a predeterminedband of frequencies are used to determine the edges. The allowed band offrequencies may be configured based automatically by image analysistechniques and/or set manually. In one embodiment, a low threshold maybe set and a high threshold value may be set, such that data valuesbelow the low threshold and data values above the high threshold may befiltered out of the image. The output of the band-limited gradientoperation 156 is output to three blocks, blocks 158, 162 and 168. FIG. 8illustrates an exemplary output of the data after the data has beenprocessed by block 168.

At block 158, the output of the band-limited gradient operation 156 isinput into a frame delay buffer. The frame delay buffer 158 compares theprevious image data with the next image to determine how far the targetmoved between images by using a correlation process, as shown in FIGS. 9and 10. One of ordinary skill in the art will readily appreciate that avariety of correlation functions may be used in accordance with aspectsof the present invention. FIG. 10, illustrates an embodiment, whereinthe HEL spot is off center. It should be noted that the track spot isvirtually unaffected by presence of the HEL spot.

At block 160, the complex conjugate of the Fast Fourier Transform (FFT)of the received image is calculated. The conjugate is output to thelogical multiplier 162 (e.g., convolution operator), which multipliesthe band-limited gradient operator data output from block 156 with theconjugate output from block 160. Thus, the logical multiplier 162essentially multiplies the present image with its conjugate. An inverseFFT is applied to the resulting product, which converts the frequencydata to spatial data (e.g., a 2-dimensional image), at block 164. Theoutput of block 164 is an image that illustrates bright spot relativeshift in position between the delayed image and the new image, as shownin FIG. 9. In this example, the bright spot (circular shape) isgenerated by the HEL beam 18.

One input to block 166 includes information on the shift in position ofthe present image. The other input to block 166 is an input from a framedelay buffer at block 170. Block 170 receives input from block 168,which is an inverse FFT applied to the band-limited gradient operatordata output from block 156 to convert the frequency data to spatialdata, at block 168. The output of block 168 is routed to a frame delaybuffer 170 and separately to a logical summer 172.

At block 166, the scene registration block determines the shift inposition of bright objects in the data. The output image is shifted fromthe old position to the new position, as shown in FIG. 10. The output ofblock 116 is summed with the output at block 168 at the logical summer172. This step establishes a reinforced image that is able to accountfor a noisy image due to environment and/or other conditions, asillustrated in FIG. 11.

At block 174, the output of the logical summer 172 is input to block174, wherein the resulting image may be subjected to furthermanipulations, such as threshold (e.g., binarizing) and centroidcalculations, as shown in FIG. 12. In FIG. 9, the HEL spot has beencentered along with the target. The output of block 174 is used fortarget positioning measurements and input into the mortar trackingalgorithm discussed below. As used herein, “threshold” refers discardingand/or deleting image values above and/or a below a certain value. Thevalue is referred to the threshold value.

Referring to FIG. 13, a block diagram of an exemplary mortar trackeralgorithm 200 is illustrated. The algorithm 200 receives the output ofblock 174 from the mortar detection algorithm 150 as an input. Theoutput of block 174 is in the form of a centroid that has beenthresholded, such that the outline of the mortar is uniform (e.g., inthe form of a silhouette), as shown in FIG. 12. At block 202, thesilhouette is compared to a list of discrete objects and measuredattributes (e.g., position, size, speed, etc.) to determine the type oftarget identified.

At block 204, the object is associated with the track to determine whichobjects are maximally likely represent establish tracks. For example,which identified objects are most like other objects that have been seenbefore.

At block 206, the centroid associated with the most likely objectbecomes a measurement that is input to a Kalman filter. A Kalman filterprovides an efficient computational (recursive) mechanism to estimatethe state of a process, in a way that minimizes the mean of the squarederror. A Kalman filter supports estimations of past, present, and futurestates. In this particular case, the Kalman filter maintains the bestestimate of track object attributes (e.g., position, velocity, size,etc.) for each detected object. For example, the Kalman filter maydetermine that the size of a target is increasing, which generally meansthat the target is coming closer to the detection system.

The Kalman filter is recursive in that the state returns to block 202,determine which objects are maximally likely represent establish tracks.When recursive process is complete and/or an object and/or track hasbeen identified the Kalman filter outputs the results to the trackmanager at block 208.

The track manager determines if new tracks are to be spawned, staletracks should be pruned and selection of the track of maximallylikelihood to be the target. For example, if the track manager is unableto associate any tracks with a known object (e.g., the object has thewrong speed and/or shape), a new track may be spawned to track theobject. If a previously identified track has object attributes that nolonger match other known objects, the track may be deemed stale andpruned (e.g., no longer monitored). When the track is identified aslikely to be the target, the tracks angle, position and measurementinformation is provided to the HEL steering controller function block330, as discussed below.

The processes discussed above are generally applicable to mortartargets. One method to destruct mortars is generally to illuminate aspot on the mortar case that heats the exterior and conductive heattransfers to the explosive filler of the mortar causing a low gradedeflagration that ruptures the case rendering the mortar inert. Such amethod is generally not applicable to unmanned aerial vehicles (UAVs).In a UAV, the above methods may cut a small hole near the center of theUAV. Such a hole may not disable the UAV and the UAV could remain athreat (e.g., the cutting of a small hole would not guaranteedisablement or destruction of the UAV. One method of destroying a UAV isto cut a wing off of the UAV. In order to accomplish this task, theaimpoint generally must be offset to a vulnerable portion of the target.Therefore, the center of the image and at least one offset point isgenerally needed to be tracked. This requires the attitude of the targetto be tracked (e.g., bank angle, yaw angle, roll angle, pitch angle,etc.).

Referring to FIG. 14 an exemplary method 250 for targeting an intendedtarget is illustrated. At block 252, data from the detector 30 isreceived. Block 252 removes speckle detected in the data. Generally, thedata is in the form of raw image and input into block 252. One ofordinary skill in the art will readily appreciate that the image may bea raw image and/or include some processing of the image prior to entryinto the block 252. At block 252, the data is low passed filtered toremove or attenuate values that are above and/or below a thresholdvalue. Such values may be caused by speckle and/or hot spots in thedetected image. For example, data that is above and/or below the averageintensity of the image may be clipped and/or attenuated.

At block 254, a fast Fourier transform is performed on the filtereddata, which converts the data from the spatial domain to a frequencydomain.

At block 256, a band-limited gradient operation is performed on thedata. The band-limited gradient operation removes the low frequenciesand high frequencies detected in the image, so that a predetermined bandof frequencies are used to determine the edges. The band-limitedgradient operation at block 206 is the same as the operation discussedabove with respect to block 156.

The band-limited gradient operation block 256 also receives band-limitedgradient data from a reference library of UAVs. The reference library ofUAVs is provided at block 258. The reference library includes allpertinent information necessary to track a desired UAV target. Forexample, the reference library includes images of each target to betracked along with one or more offset points to identify one or morevulnerable points of the target. The vulnerable points may be stored inany desired manner. For example, the reference library may includetarget centered coordinates that may be used by offset the aimpoint.

At block 260, a fast Fourier transform is performed one or morereference objects from the reference library, which converts the dataassociated with targets in the reference library from the spatial domainto a frequency domain.

At block 262, a band-limited gradient operation is performed on the datafrom the reference library. The band-limited gradient operation removesthe low frequencies and high frequencies detected in the image, so thata predetermined band of frequencies are used to determine the edges. Theoutput of the band-limited gradient operation 262 is output to block 256and block 264. The band-limited gradient operation at block 262 is thesame as the operation discussed above with respect to blocks 156 and256.

The band-limited gradient operator 256 combines the image data with thereference library data and routes combined image data to block 268 andblock 270.

At block 268, an inverse FFT is applied to the filtered data, whichconverts the frequency data to spatial data (e.g., a 2-dimensional imagecorrelation surface) for use by the beam steering architecture, asdiscussed below. The image output at block 268 is a band-limited, edgedetected image, which may be similar to FIG. 8 discussed above withregard to a mortar target.

At block 264, the complex conjugate of the band-limited data associatedwith the reference image is calculated.

At block 270, a convolution operation is performed on the complexconjugate of the band-limited data with the combined band-limited datafrom the present image and the band-limited data associated with thereference image.

At block 272, an inverse FFT is applied the output of the convolutionoperation to obtain a correlation surface, which indicates scoringcriteria for pose detection, peak position localization of center ofgravity of the target, etc. The output of block 272 is a correlationsurface, which is output for use by the beam steering architecture, asdiscussed below.

The principle of operation of the beam director subsystem 12 isdiscussed referring to FIGS. 15A-15D. The bore sight 110 depicted in theimages may correspond to the center of the detector 30. Referring toFIG. 15A, the centroid of the object pair, which corresponds to thefirst and second portions 111 of the HEL beam, is denoted with thereference “x” indicates bore sight error between the HEL beam 18 and thetrack detector 30. The error is given in terms of elevation (el)alignment error and azimuth (az) alignment error. The object separation(less=longer) indicates focus range. The processor generally calculatesa centroid (which corresponds to the “x” reference in FIG. 15A)corresponding a HEL position (x) that corresponds to an equidistantpoint located between the first portion 111 of the HEL beam and thesecond portion 111 of the HEL beam received by the detector 30. Forexample, the processor determines a number of pixels that the HELposition is offset from the center point of the detector to determineHEL beam misalignment. In one embodiment, processor also determines anangle of divergence between the first portion of the HEL beam and thesecond portion of the HEL beam.

Referring to FIG. 15B, a target 112 enters the field. The weapon systemplaces the target in field of view of detector 30; provides rangemeasurement to adjust focus of the primary and secondary mirrors; andthe processor measures the information received at the detector toachieve focus range and adjust accordingly. For example, the portion ofthe tracking beam received by the detector and a centroid is calculated.The processor then calculates a number of pixels that the centroid isoffset from a center point of the detector 30 to determine tracking beammisalignment.

With this information, the processor calculates target and measures boresight error. Referring to FIG. 15C, the processor generates a controlsignal to steer the HEL beam to the airborne target based upon thedetermined relationship. For example, a guidance filter directs faststeering mirror 44 to steer HEL beam 18 to target position. Referring toFIG. 15D, the target is engaged with the HEL beam 18.

Referring to FIG. 16, an exemplary beam steering architecture 300 isillustrated. The beam steering architecture may include a UAV trackchannel 302 and a mortar track channel 304, identified in dashed lines.A track source selector 306 is used to determine, which channel isactive. For example, when selector 306 is in position “A”, the UAV trackchannel is operative. When the selector 306 is in position “B”, themortar track channel is operative, when the selector is in position “C”,neither the UAV track channel nor the mortar track channel is operative.When the selector is in position “C” track radar data from the PhalanxGun System is operative. When the selector 306 is in position “D”, theselector is not operative. The track source may be manually controlledand/or controlled by a processor.

The following parameters may be input to the beam steering architecture:inertial measurement units output from gyroscope triads 100, 102 (e.g.,IMU 1&2 Gyros) 308, inputs relating to azimuth and elevation 310 from ahost platform (e.g., a Phalanx Gun system manufactured by Raytheon oranother weapon platform), track camera information 312, and track radardata 314. One of ordinary skill in the art will readily appreciate thatthe above inputs are exemplary in nature and that a beam steeringarchitecture may receive additional inputs and/or a differentcombination of inputs than described.

The gyroscope information 308 and azimuth/elevation information 310 isinput to a navigator 316. The navigator 316 uses this information todetermine where the HEL is pointing in three-dimensional space. Thenavigator 316 may be a Kalman filter that estimates gyroscope bias, forexample.

The following description of the beam steering algorithm will assumethat the track source selector is in position “A”. The output from thenavigator 316 is input to the T_(F2E) block 318, which transformscoordinates from the focal plane of the camera to earth-centeredcoordinate system. The output from the navigator 316 is also received atblock 320 for a determination of the UAV target pose detection andcenter of gravity localization. The output of block 268 from FIG. 14 isalso received by block 320. Block 320 determines the target posedetection and center of gravity localization of the UAV, as explainedabove with respect to FIG. 14. The output of block 320 is transferred toattitude filter block 322 and to T_(F2E) block 218.

The attitude filter block 322 receives input from block 320 thatcorresponds to the UAV target pose detection and center of gravitylocalization block 324. Block 324 corresponds to the inferred attitudeestimator. The inferred attitude estimator receives state informationfrom the radar filter, at block 326. The radar data information includesX, Y, Z position measurements from the radar data, at block 314. Inblock 326, range from radar data block 326 is combine with two anglesfrom a camera to obtain a pseudo-measurement (not a direct measurementin free space, but a combination of a 2D measurement and a 1Dmeasurement which yields a pseudo X, Y, Z measurement that is used toupdate the Kalman filter 332.

The inferred attitude estimator 324 estimates a velocity andacceleration from the position. From this estimation, attitudeinformation associated with the target may be inferred, assuming thetarget is a winged aircraft-type target. For example, if a target flyingstraight and level with no acceleration and constant velocity and notturning, an inference may be made that the wings will be level. Thisinference is used to reduce the amount of searching in the attitudefilter in the pose detection portion. That is, an exhaustive search ofevery possible combination of yaw, pitch and roll does not have to besearched, which reduces the number of possible combinations of yaw,pitch, and roll combination in the library. Since it is known that, inthis example, there is no acceleration; only pose coordinates between+/−10 degrees need to be searched to final a valid pose estimate.

Based on the information provided from block 326 and 324, the attitudefilter 322 outputs an attitude estimate to the aimpoint manager 328. Theaimpoint manager 328 also receives state information from a Kalmanfilter 332. The Kalman filter 332 is a nine state filter that providesupdates of state variables associated with position, velocity andacceleration associated with the target. The Kalman filter 332 receivesinput from pseudo-measurement block 334. The pseudo-measurement block334 receives inputs from the T_(F2E) block 318, which transformscoordinates from the focal plane of the camera to earth-centeredcoordinate system range and covariance data from the radar filter 326.Based on these inputs center of gravity state estimates are made. Thisinformation may be updated at predetermined times, based on every newimage or any other desired manner to effectively track a UAV target.

Now operation of the beam steering architecture will be described inconnection with the mortar track channel 304. As set forth above, themortar track channel 304 is operative when the track source selector isin position “B”, as illustrated in FIG. 16.

The output from the navigator 316 is input to the T_(F2E) block 336. Theoutput from the navigator 316 is also received at block 338, whichcorresponds to the mortar tracking algorithm discussed above inconnection with Block 208 of FIG. 13. The output of the mortar trackingalgorithm block 338 is received by T_(F2E) block 336. The T_(F2E) block336, which receives information from the navigator block 316 and themortar track block 338, which transforms coordinates from the focalplane of the camera to earth-centered coordinate system.

The output of the T_(F2E) block 336 is received by thepseudo-measurements block 340 along with range and covariance dataprovided by the radar filter block 326. The pseudo-measurement block 340receives inputs from the T_(F2E) block 336, which transforms coordinatesfrom the focal plane of the camera to earth-centered coordinate systemrange and covariance data from the radar filter 326. Based on theseinputs center of gravity state estimates are made. This information maybe updated at predetermined times, based on every new image or any otherdesired manner to effectively track a mortar target.

The updated information is sent to the Kalman filter block 342. Theoutput of the Kalman filter block 342 is made available to the aimpointmanager block 328, which determines where to steer the HEL 18 andtransfers the coordinates to steering controller block 330 for use bythe high rate extrapolator and steering mirror controller, which is alsoreferred to herein as the “HEL Steering Controller”, “Beam SteeringController” and/or “steering controller”. The high rate extrapolator andsteering mirror controller block 330 functions to output steering themirror rate commands to control steering of the HEL 18 by providingcontrol signals to mirrors 38, 40. The steering controller functionblock 330 is operatively coupled to the processor. The steeringcontroller function block 330 may be a component of the processor 20(e.g., a component of the computer system), as illustrated in block 36of FIG. 2 or be remotely located from the processor 34.

Although the invention has been shown and described with respect tocertain preferred embodiments, it is obvious that equivalents andmodifications will occur to others skilled in the art upon the readingand understanding of the specification. The present invention includesall such equivalents and modifications, and is limited only by the scopeof the following claims.

1. A beam director system comprising: a source of electromagneticradiation for generating a high energy laser (HEL) beam; a secondarymirror for receiving the electromagnetic radiation and reflecting theelectromagnetic radiation to a primary mirror for output of the HEL beamthrough a housing, wherein the secondary mirror is curved and expandsthe electromagnetic radiation received from the source prior tooutputting the HEL beam from the primary mirror; a track telescopecoupled to the housing, wherein the track telescope has a track detectorconfigured to receive a first portion of the electromagnetic radiationof the HEL; a first reflecting surface to route the first portion of theelectromagnetic radiation of the HEL beam to the track detector; asecond reflecting surface to route the first portion of theelectromagnetic radiation of the HEL beam to the first reflectingsurface and a third reflecting surface to route a second portion of theelectromagnetic radiation of the HEL beam to the track detector; and aprocessor coupled to the track detector and a steering controller of theHEL beam, wherein the processor processes the first portion of theelectromagnetic radiation to steer the HEL at an associated target. 2.The system of claim 1, wherein the first reflecting surface is apentaprism.
 3. The system of claim 1, wherein the second reflectingsurface is a pentaprism.
 4. The system of claim 1, wherein the firstreflecting surface and the second reflecting surface are opticallycoupled to a first edge of the primary mirror.
 5. The system of claim 1,wherein the third reflecting surface is a retroreflector.
 6. The systemof claim 1 further including a fourth reflecting surface to route thesecond portion of the electromagnetic radiation of the HEL beam to thethird reflecting surface.
 7. The system of claim 6, wherein the thirdreflecting surface and the fourth reflecting surface are opticallycoupled to a second edge of the primary mirror, wherein the first edgeand the second edge are on opposing sides of the primary mirror.
 8. Thesystem of claim 1 further including an illuminator for generatingelectromagnetic radiation to be directed at the associated target. 9.The system of claim 8, wherein the track detector is also configured toreceive the electromagnetic radiation reflected from the airbornetarget.
 10. The system of claim 1, wherein the housing is made ofaluminum.
 11. A method of aiming a high energy laser (HEL) beam, themethod comprising: generating electromagnetic radiation for use as a HELbeam to be directed at an airborne target from a source ofelectromagnetic radiation; reflecting the electromagnetic radiation offof a secondary mirror and a primary mirror for output of the HEL beamthrough a terminal end of a housing, wherein the secondary mirror iscurved and expands the electromagnetic radiation received from thesource prior to outputting the HEL beam from the primary mirror;detecting a first portion of the HEL beam prior to output from theterminal end of the housing at a track detector and detecting a secondportion of the HEL beam prior to output from the terminal end of thehousing at the track detector, wherein the first portion and the secondportion correspond to opposing sides of the HEL beam; processing thefirst portion of the HEL beam and the second portion to control asteering controller of the HEL to steer the HEL at an associated target.12. The method of claim 11, wherein the step of detecting the firstportion of the HEL prior to output from the terminal end of the housingincludes reflecting the first portion of electromagnetic radiation ofthe HEL beam to the track detector with a first reflecting surface. 13.The method of claim 12 further including reflecting the first portion ofthe electromagnetic radiation of the HEL beam from a second reflectingsurface to the first reflecting surface.
 14. The method of claim 13,wherein at least one of the first reflecting surface and the secondreflecting surface is a pentaprism.
 15. The method of claim 13, whereinthe first portion of electromagnetic radiation and the second portion ofthe electromagnetic radiation are obtained from opposing sides of theprimary mirror.
 16. The method of claim 15 further including generatingelectromagnetic radiation from an illuminator secured to the housing,wherein the illuminator outputs electromagnetic radiation used to trackthe associated target.
 17. The method of claim 16 further includingdetecting the electromagnetic radiation used to track the associatedtarget at the track detector.
 18. The method of claim 11, wherein thestep of detecting the second portion of the HEL prior to output from theterminal of the housing includes reflecting the second portion ofelectromagnetic radiation of the HEL beam to the track detector with athird reflecting surface.